Conventional fireplaces are inefficient sources of heat for the room in which they are located primarily because the fire draws air from the room and large amounts of outside air into the house to meet the combustion requirements of the fire. This causes drafts of cold air along the floor of the room and the cooling of the house.
In my U.S. Pat. No. 4,357,930, there is disclosed a fireplace heating system for heating the room air by the use of a compact heat exchanger mounted at the top portion of the combustion chamber of the fireplace to extend across the location where the chimney flue connects with the top portion of the combustion chamber. A fan is provided for circulating room air through the heat exchanger in a manner so that the hot combustion gases heat up the room air being circulated therethrough.
In accordance with the present invention, there is provided an improved heat exchanger device that increases the efficiency and performance of fireplace heating systems. The heat exchanger device in accordance with the invention is particularly adaptable to homes heated by heat pumps. Heat pumps are relatively inefficient at low outside temperatures (below 40.degree. F.) and are normally supplemented with electric resistance heating, especially in the northern regions of the United States. Electric resistance heating is very expensive to operate. By the use of the heat exchanger device in accordance with the invention, it is possible to drastically reduce the "electric demand" on wiring and power plants during critical winter time "cold snaps".
The basic purpose of the device in accordance with the present invention is to extract substantial heat energy from the fire in the fireplace during these periods of very low outside temperatures by the use of a novel heat exchanger. This device, for instance, may be used in conjunction with a ceramic gas log burning bottled propane in a conventional fireplace, this type of burner being well known in the art. Normally, these gas logs are added to existing fireplaces for the convenience and aesthetic visual pleasure of the gas flame.
By using the novel heat exchanger device in accordance with the invention in a heating system as described hereinafter, it is possible to make the gas log burner a practical source of environmentally clean thermal energy, especially in cold winter climates. Moreover, the novel arrangement in accordance with the invention may also be applied to the more conventional wood-burning fireplace. As will be described hereafter, one of the features of the heat exchanger device in accordance with the invention is that it is readily adaptable to existing fireplaces and can even utilize existing fireplace screens or covers.
The optimum employment of the heat exchanger in accordance with the invention is in a heating system that utilizes outside air for combustion, a glass cover for the fireplace opening, and, preferably, a means for distributing the heat coming from the heat exchanger to the entire home or other structure. If a heat pump or central air conditioning system has been installed in the home whereat the heating system is used, it would be desirable to have the heat exchanger device function as a supplemental heat source, using a booster fan installed in the return duct of the room where the fireplace is located forcing the warm air from the fire place into the plenum chamber and subsequently circulating it through the entire house.
While the description of the invention illustrates that the invention can be applied to an existing conventional fireplace with its conventional glass screen or cover, it will be noted that the invention can also be applied to new construction, which might utilize a single heat exchanger (instead of the pair of heat exchangers described) in a modern type of "free-standing" fireplace with a glass enclosure on all four sides.
Another feature of the invention is that all of the components of the heat exchanger device are designed and arranged so that they can be manufactured and assembled economically and so as to result in a viable commercial product pleasing in appearance and economical to operate.
Briefly stated, a fireplace heating system in accordance with the invention includes a heat exchanger means mounted at the top portion of the combustion chamber to extend across a location where the chimney flue connects with the top portion of the combustion chamber, and fan means for circulating room air through the heat exchanger. The heat exchanger comprises means defining a heat exchange passage for the flow of room air and means for defining a second heat exchange passage for the flow of combustion gases in a vortex flow from the combustion chamber to the chimney flue, the heat exchange passages being arranged in heat exchange relationship so that the hot combustion gases heat up the room air being circulated through the heat exchanger by the fan means. In accordance with a preferred embodiment, there are provided two of the novel heat exchangers which are arranged in side-by-side relationship to conform with the rectangular shape of the plan view of a traditional fireplace. In addition, the device in accordance with the invention is designed to be adjustable and thus readily adaptable to retrofitting various sizes and shapes of existing fireplaces.
An alternative preferred embodiment is provided which is easier to manufacture. This alternative preferred embodiment works in a manner similar to the first preferred embodiment by converting the thermal energy in a wood fire or gas log fireplace in a highly efficient manner to warm the room air circulating through the heat exchanger assembly and through the various chambers and passageways of the heat exchanger assembly.
To obtain this high efficiency, I place a heat exchanger between the heat source burning flame, and the exhaust gas exit, the chimney. The heat exchange assembly is designed to extract the maximum amount of heat by delaying the removal of the exhaust gases, and by causing the hot exhaust gases to dwell in the region of the heat exchanger, a region of high heat conductivity, while maintaining high heating gas velocity for good heat exchanging. This is accomplished through the novel use of an exhaust gas "spin chamber". As in my first preferred embodiment the lighter hotter spinning exhaust gases tend to spin on the inside of the "spin chamber", contacting the aluminum heat exchanger wall, while the denser cooler gases centrifuge to the outer steel cylinder wall of the "spin chamber". A difference between this second preferred embodiment and the first preferred embodiment, is that the second preferred embodiment is simpler and less expensive to construct and assemble.